Patent Document No. 1 discloses a conventional barrier unit. FIG. 6 is a cross-sectional view illustrating a barrier unit 101 as disclosed in Patent Document No. 1.
At the center of a frontend plate portion 101A, there is a window 101a that makes an optical path with respect to a lens 109. A set of barrier blades 104, which is arranged in front of the frontend plate portion 101A, opens and closes the window 101a. When the barrier blades 104 are open, a shutter opens and closes on a shutter plate 110, thereby getting shooting done.
In this barrier unit 101, when the barrier blades 104 are fully opened or closed, a barrier blade drive ring 102 protrudes toward the direction from which light is coming, thereby pressing the barrier blades 104 against a barrier protective cap 108. As a result, sand or any other foreign matter will not easily enter the gap between the barrier blades 104 and the barrier protective cap 108.                Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 9-61887        